The public health significance of many medical, psychiatric, and neurological conditions and/or disorders is often overlooked, probably because of their episodic nature and the lack of mortality attributed to them. However, some medical conditions, such as headaches and facial pain, are often incapacitating, with considerable impact on social activities and work, and may lead to significant consumption of drugs.
Headaches are one of the most common ailments, and afflict millions of individuals. The specific etiology of headaches may be difficult to pinpoint. Known etiology of headache pain include trauma and vascular, autoimmune, degenerative, infectious, drug and medication-induced, inflammatory (sarcoid), neoplastic (primary or metastatic), metabolic-endocrine, iatrogenic (such as post-surgical), musculoskeletal and myofascial causes. Even if the condition underlying the headache pain is identified and treated, headache pain may still persist.
Diagnosis of headache pain will typically include an identification of one or more categories of headaches. There are a variety of different headaches with different features. Migraine headaches, as defined by the International Headache Society (IHS) Classification, are typically unilateral, throbbing headaches lasting from four to seventy-two hours. Migraines are often accompanied by nausea, vomiting, light sensitivity and/or noise sensitivity. Females suffer from migraines more than males by an approximate ratio of 3:1. Migraine headaches can be further subdivided and sub-classified into a number of different categories, such as, but not limited to, for example, migraine with aura, migraine without aura, transformed migraine, and retinal migraine.
Migraines have traditionally been treated with medications to prevent their recurrence and to alleviate acute pain and associated symptoms, such as nausea and vomiting. Non-invasive modalities of migraine treatment, which may be used alone or in combination, have included: diet modification, which may include the avoidance of known headache triggers (such as certain foods); biofeedback and relaxation techniques as well as other psychological modalities; acupuncture; chiropractic manipulation; and physical therapy. Invasive therapeutic procedures have also been implemented and have included localized anesthetic blocks as well as neurosurgical interventions, such as nerve and ganglion transections and/or resections. However, use of those invasive techniques has typically been reserved for patients who have been unable to tolerate non-invasive procedures or who suffer from refractory headaches inadequately controlled with non-invasive methods. Invasive techniques are not more readily employed because they have been known to cause undesirable side effects and pose risks of infection and/or physiological damage to nerve tissues.
Currently, the highest known success rate (approximately seventy percent) in alleviating the pain of an acute migraine attack has been achieved using triptan class medications. Unfortunately, the effectiveness of each therapeutic modality typically varies widely between individual migraine sufferers and, irrespective of the treatment modality used, the suppression of migraine pain is often short-lived, with the pain recurring at levels which are typically less but sometimes equally or rarely more intense than before treatment. Many migraine sufferers find that their migraines are resistant to conventional treatment. In some cases, patients suffer from migraines on a continuous daily basis rather than on an episodic basis. Accordingly, a major emphasis for migraine treatment has been on prevention techniques.
Newer methods for treating a variety of neurological disorders have included various electrical stimulation techniques. For example, U.S. Pat. No. 5,540,734 to Zabara describes a suggested therapeutic modality for a variety of medical, psychiatric and neurological disorders, including migraines, in which modulating electrical signals are applied to either or both of the trigeminal and glossopharyngeal nerves using electrodes. The principle behind these approaches is to disrupt or modulate abnormal neuronal transmissions in the nervous system through the application of the modulating electrical signals.
Cluster headaches are so termed due to their repeated occurrence in groups or clusters. Cluster headaches are much less common than migraines. Migraine sufferers outnumber cluster headache sufferers by a ratio of approximately 100:1. Cluster headaches are characterized by intense, stabbing pain usually starting in the region of an eye or temple and localizing to one side of the face. Autonomic features such as lacrimation, nasal congestion, ptosis, conjunctival injection and pupillary changes are common in cluster headaches, which occur predominantly (approximately 90%) in males and usually start in the third or fourth decade of life. It is believed that the ingestion of alcohol may trigger the onset of cluster headaches.
IHS criteria indicate that episodic attacks of cluster headaches may last up to 90 minutes and may occur as many as six times per day. Cluster headaches typically occur in cycles lasting weeks to months and then spontaneously remit. Frequently, cluster headaches have a seasonal correlation, with their onset occurring more often in the fall and spring. While there are wide variations in the start of cluster headache cycles between headache sufferers, the cycles experienced by individual headache sufferers frequently follow a defined pattern with little deviation. The headaches usually occur at night, and often awaken the headache sufferer from sleep. It is not unusual for individual headache sufferers to experience the onset of cluster headaches at the same time during the night over repeated nights.
Because of the typically short duration of cluster headaches, therapies designed to abort the pain of an acute attack must have a quick onset of action. Such therapies have included oxygen inhalation and injections of medication, such as dihydro ergotamine (DHE), ketorolac, or sumatriptan. Non-invasive therapies used to treat cluster headache pain and prevent their recurrence have included use of medications including ergot derivatives, varapamil, lithium, steroids, and sodium valproate; psychological intervention with biofeedback and relaxation techniques; and acupuncture. Anesthetic agents (such as Lidocaine) have been applied to the sphenopalatine ganglia, either directly, using a syringe, or indirectly, by soaking a long cotton swab in the anesthetic and placing the swab intranasally adjacent to the sphenopalatine ganglia, such that the anesthetic diffuses through the nasal mucosa to affect the SPG. Invasive approaches for the treatment of cluster headaches have included localized anesthetic block, surgical resection, radiofrequency, alcohol/phenol infiltration, radiosurgery and cryotherapy of the sphenopalatine ganglia and the trigeminal nerve and ganglion. The invasive approaches for treating cluster headaches are typically used only in headache sufferers who cannot tolerate the non-invasive methods of treatment or in whom the cluster headaches are refractory and inadequately controlled with non-invasive methods.
Neuralgias, such as trigeminal, sphenopalatine, and occipital neuralgias, may start at any age, although trigeminal neuralgia is more common among the elderly. From a pathophysiological standpoint, neuralgias, which are types of pain associated with a particular nerve, always originate from and are transmitted by the involved nerve. Accordingly, neuralgias may be caused by direct injury to nerves in the form of trauma, infection (such as herpes), neuroma formation or demyelination. The pain of a neuralgia may be brief and paroxysmal or continuous, and numerous attacks may occur throughout the day. Neuralgias do not feature seasonal or diurnal patterns in the onset of pain. In contrast to cluster headaches, trigeminal neuralgia often has an associated “trigger zone” on the face which can trigger the onset of the pain. Sphenopalatine neuralgia often has autonomic features that are not commonly found in other neuralgias. In occipital neuralgia, the occipital nerve is usually tender to palpation and pain can be manifested anywhere along the course of the nerve.
Neuralgias, like migraines, have been treated using medication, invasive procedures, and, rarely, electrical stimulation of cranial nerves which are part of the central nervous system. None of the medications used in treating neuralgias have generally been effective in treating cluster headaches, other than sodium valproate.
The use of medications to treat the above-described conditions and other types of medical, psychiatric, and neurological conditions and/or disorders can result in systemic side-effects of wide-ranging severity. Invasive techniques used to destroy tissues, such as lesioning, resecting, freezing, or burning, are typically non-reversible, and the treatment cannot be adjusted once applied. Destruction of the nerve tissue may itself lead to significant side effects, such as deafferentation pain.